Vertical Mist Nets

We trialed several vertical configurations (for example, T-angle, several different V-angles, straight lines) of four- and two-shelf mist nets. Two-shelf mist nets, also known as puddle nets, were more effective at capturing TBLO than were four-shelf mist nets in most situations. Two-shelf mist nets were less visible, especially during windy conditions, and they were quicker to deploy. We used a combination of four-shelf and two-shelf mist nets while attempting to capture TBLO along shorelines of waterbodies, but we primarily used two-shelf mist nets for capture attempts in open habitats after initial field trials using four-shelf mist nets were unsuccessful.

To capture displaying male TBLO, the most effective arrangement was a V formation of two-shelf mist nets with an audio lure placed off center of the net junction (fig. 4). The precise location where we set up each mist net V formation depended on the behavior of the bird, the weather, and other factors. If a displaying male did not approach the trapping area within about the first 20 minutes, we typically did not capture that individual. As the season progressed, we used 20 minutes as a benchmark to determine when to terminate a capture attempt using the V formation. We also attempted to flush TBLO into the net when they were near the net junction, either by tossing a benign object (for example, a soft frisbee or foam airplane) towards the general trapping area (but not at the bird) or by running toward the bird. After several attempts, mostly with displaying males, we determined that these flushing techniques were ineffective and not worth continuing.

We also tested vertical mist nets away from active territories over baited sites and near areas where TBLO congregated (for example, water or bare ground). At baited sites, we used the same V formation described above, but usually with a more acutely (less than 90 degrees) angled V surrounding the bait. Trapping at large waterbodies posed a different challenge: directing TBLO use to the part of the shoreline containing the nets as opposed to the part of the shoreline with no nets. First, we observed which parts of the shoreline TBLO tended to use before net placement and then placed multiple mist nets near the water’s edge in this section. Second, we determined that birds needed to be deterred from other parts of the open shoreline to use the part of the shoreline with the mist net arrangement. We did this by placing butterfly nets along the water’s edge or by sitting along the shoreline (fig. 5). Other items, like flagging tied to a short stick, would likely function similarly by encouraging TBLO to use the shoreline near the mist net arrangement. During water and baited site capture attempts, to increase efficiency of time spent in the field, we often completed other field activities nearby, such as nest searching, and visually inspected nets every 15–30 minutes for captured birds.

We used vertical two-shelf mist nets to capture fledglings that could sustain short flights but that could not be captured via a hand net We located the fledgling, placed a net nearby, then slowly “herded” the fledgling towards the net, often using hand nets to extend our arm lengths for more effective herding. As we got closer to the net, we narrowed our spacing between researchers and attempted to flush the fledgling into the net. We terminated the effort if unsuccessful after roughly three attempts.

Vertical two-shelf mist nets also were used near nests for “on-nest” captures. We generally placed vertical mist nets about 1 m away from nests. We trialed this method to capture incubating females, as well as both sexes while they provisioned food to nestlings. For incubating females, we waited about 15 minutes after deploying the net before walking towards the nest to flush the female towards the net. We were successful in capturing one incubating female using this method, but only one attempt to flush the female was usually possible. If we failed on the first flush attempt, the female seemed to be aware of the net and would fly over or around the net on subsequent attempts. For nests with nestlings, we did not attempt to flush individual adults into the vertical mist net. Although this method occasionally led to a successful capture, we determined that placing the mist net horizontally (refer to the “Horizontal Mist Nets” section) led to less time spent near the nest and quicker, more efficient captures.

Bait

We used commercial songbird seed mix and white millet as bait to attract TBLO at certain prairie sites. We used bait in areas where we observed groups of TBLO; bait locations were near water, on patches of open bare ground, and on the territorial edges of displaying males. Our bait sites occasionally attracted other bird species and small mammals (for example, ground squirrels and mice), which may be a concern for landowners and managers and may increase the possibility of incidentally capturing other species; for example, bait sites may attract small mammals that depredate crops and possibly TBLO nests. It would be prudent to maintain clear communication with landowners and managers before using bait and to consider risks of introducing nonnative plant species into the landscape. We did not use bait near known nests, and we made sure to place bait on the boundaries (rather than at the center) of male territories when territorial boundaries were known. We used a variety of capture methods near and over bait including walk-in traps, bow nets, and vertical and horizontal mist nets. We sometimes used conspecific audio lures (refer to the “Conspecific Audio Lures” section) when we were trapping in baited areas as a way of increasing efficiency to attract adult TBLO, but we are unsure if this addition was worthwhile.

When starting to bait a new area, it was useful to spread the seed around the intended capture site to increase the chances of birds finding the bait (about two to five times the area of the intended capture location). Once birds were observed foraging on the bait, we concentrated the bait into smaller areas where the trap would eventually be placed, and we often created a small depression, about the size of a fist, where the seed was deposited. We used white millet for our concentrated bait piles because animals were less likely to scatter millet than the songbird seed mix, presumably because of the uniform small size of millet or preferences for certain seeds in the mix. We observed a hierarchy of visitors at the bait piles. Early on, ground squirrels and birds larger than TBLO seemed to relegate TBLO to the periphery of the bait piles. Eventually, when the ground squirrels and larger birds left the bait area, even if just temporarily, TBLO would begin to feed more at the center of the bait pile. We placed camera traps near some of our bait sites to assess visitation by TBLO and to determine the optimal timing for capture attempts.

There are several considerations when using bait to attract TBLO. First, attracting birds to bait stations takes time (to allow birds to find and habituate to bait sites), so baiting would generally need to begin several days before an anticipated TBLO capture attempt. Second, maintaining a consistent supply of bait was often challenging because of seed consumption by ground squirrels and other bird species (for example, brown-headed cowbirds and Euphagus cyanocephalus [Brewer’s blackbirds]). This method also increases the chances of capturing other bird species in traps near bait. Additionally, wet weather and its effects on the roads at our field sites limited our ability to restock bait regularly. Automatic seed feeders might be useful in future efforts, especially feeders designed to only allow seed consumption by birds. Third, the use of bait aggregates individuals and species across taxonomic groups, which may increase risk of transmission of diseases such as avian influenza. Finally, providing supplemental food could introduce additional forms of bias that may be counterproductive in a study of population vital rates.

Conspecific Audio Lures

We used audio recordings of TBLO vocalizations from Xeno-canto (https://xeno-canto.org) and the Macaulay Library at the Cornell Lab of Ornithology (https://www.macaulaylibrary.org) as conspecific audio lures. Some of the recordings we played on repeat, and some we combined to create unique audio tracks. After a few weeks of trials, we settled on the use of self-mixed tracks that were a combination of TBLO songs and calls that we interspersed with about 20–30 seconds of silence. These audio tracks were played on repeat during capture attempts, and they included the following recordings from the Macaulay Library catalog: ML191116, ML191119, ML191756, ML169500, and ML504310521. We also created an additional audio track of TBLO vocalizations from audio recordings made by field staff from our field sites during the 2022 season: ML457153121, ML457151001, ML457150151, and ML455900151. These vocalizations were recorded using a Marantz PMD661 MKIII solid-state digital recorder (48-kilohertz sampling rate, 24 bit) with a Sennheiser ME62/K6 microphone and a Telinga Pro Universal parabola. We felt that the silent audio breaks were useful because they allowed birds time to inspect the speaker (during capture attempts) and reduced habituation to the repeated recording. Audio lures were good at drawing the interest of territorial male TBLO, but females displayed little interest. We also recorded vocalizations from a hatch-year TBLO, and we subsequently used that recording to capture a male TBLO associated with 8–10-day old fledglings. We had opportunistically recorded an 8-day old nestling TBLO vocalizing in-hand on a previous date and location, but the recording had considerable background noise that was difficult to remove. Higher quality recordings of hatch-year TBLO, including begging and alarm calls, would likely aid future TBLO capture attempts for adult birds caring for young.

Visual Decoys

We tested several visual decoys including conspecific TBLO, heterospecifics, and potential predators with and without audio lures. We used a variety of painted clay TBLO decoys (both male and female) and a preserved specimen of a female Calcarius lapponicus (lapland longspur). We occasionally attached decoys to a motor modified from the Lucky Duck Lil’ Critter Predator Decoy (https://www.luckyduck.com/lil-critter/) to provide the visual decoy with subtle movements. Our observations indicated that TBLO that were targeted for capture focused more on the audio lures than to the visual lures and decoys (both conspecific and heterospecific) during our trials. We eventually stopped using any of the TBLO visual decoys as they did not seem to improve the odds of a successful capture. We did not have access to a TBLO specimen nor were any of our clay decoys feathered, which may have hampered the success of our TBLO decoys during these trials.

Predator decoys were effective at creating disturbances that invoked inspection and defensive behaviors (for example, swooping) by TBLO adults. We tried a few different predator decoys. First, we used a ground squirrel specimen attached to the previously mentioned motor (fig. 7). Inspection and swooping behaviors were exhibited only when the moving squirrel decoy was placed near a nest, as opposed to greater than or equal to 5 m from any known nests. Early in the breeding season, we also trialed the use of a plastic common raven placed on a T-post perch. We accompanied our raven decoy with an audio recording of raven vocalizations from Xeno-canto (XC36492). TBLO did not respond to the raven decoy or vocalizations during those trials. Later in the season, we trialed the raven again, but without the perch, and observed inspection behaviors from horned larks, Calcarius ornatus (chestnut-collared longspurs), and TBLO (fig. 7A–C); however, we observed that individuals would only approach the plastic raven decoy during the initial inspection, after which individuals maintained a distance that was not useful for our capture methods. The lack of interest early in the season towards the perched raven decoy may have been because perches are uncommon in this open landscape, the general unfamiliarity with ravens as a predator (they are uncommon in this landscape), or the possibility that TBLO had not yet established territories. Lastly, we also trialed an aerial predatory bird kite to flush birds and solicit mobbing behaviors that would attract them towards the kite. During our trials, we did not observe any response to justify further use of this method (fig. 7A–C).

Other Capture Methods

In addition to the previously mentioned capture methods, we also used a variety of other trap types in our capture trials. We trialed the use of bow nets and walk-in traps to capture TBLO at nests and over bait (fig. 8A–C). Although these traps allowed for selective captures using a remotely triggered mechanism, visibility of the trap and trapping area was often obscured by vegetation and topography, making these methods challenging. In our experience, TBLO tended to land away from the lure or nest and then approach it via walking for several meters. This meant having an unobscured visual of the trapping area was particularly important. We tried using blinds (for example, popup and layout) to aid in our observation of the traps, but we did not find that blinds substantially increased our visibility of the trapping area once vegetation had grown more than several centimeters tall. Adding a live video feed for visual observation by a person in a blind 10–30 m away from a trap had limited success as topography limited the wireless connection of the feed. Use of a camouflaged endoscope camera may be more suitable for this task; however, bow nets and walk-in traps may still prove useful for targeting specific individuals provisioning young. TBLO did not seem deterred by blinds, and we were able to capture individuals successfully with these setups; however, the increased deployment time and potential for vegetation to still obscure visibility, especially later in the season, detracted from the efficiency of using bow nets and walk-in traps with blinds. Unless a selective capture is required, other methods would likely be more efficient. A passive walk-in trap (the trap is triggered by the target bird rather than by a remote mechanism) would not require a visual of the target bird and may work as well, but we did not trial this method.

We also used hand nets (butterfly nets) to capture fledglings that could not sustain flight or that could not be captured by hand. We did not trial hand nets for capturing incubating females because the dropped mist net method allowed a larger capture area to ensure coverage of the nest and nest vicinity and reduced risk of injuring the target bird (refer to the “Horizontal Mist Nets” section). We mostly used hand nets to direct birds towards vertical mist nets (refer to the “Vertical Mist Nets” section).

Finally, we used noose mats at nests and near bait sites or audio lures. We captured one adult female by covering the entryways to the nest with noose mats (fig. 9). In this instance, the female was able to return to the nest to incubate without entanglement, but upon our approach to check the mats, we observed her leg get caught as she left the nest. We were unsuccessful using noose mats near bait sites and audio lures. In these instances, birds did not walk over the noose mats to access bait or investigate the audio lure, thereby eluding capture. Although the smaller size of our noose mats was ideal for surrounding nests and their more obvious entryways, the smaller size meant that large areas near bait sites and audio lures were not covered by mats. Noose mats that are larger than those that we trialed (our mats measured about 20 square centimeters) would cover more area surrounding bait sites or an audio lure, which may be beneficial. Additionally, noose mats do not work well in tall vegetation because they are difficult to deploy properly and because the vegetation reduces visibility of the mat. Lastly, construction and maintenance of noose mats can be time consuming. Although we trialed a variety of capture methods, our list of methods was not exhaustive.

Adult Captures

We banded 32 adult TBLO during the 2022 field season and 1 adult in 2023 (table 5). Most adult birds were marked with a transmitter (n=24; table 5). We attempted to distribute captured individuals evenly among the different marking techniques and habitat types (table 4), including a cohort of individuals with only color and metal bands to serve as a comparison with individuals marked with transmitters. Lotek NanoTags and CTT LifeTags were evenly distributed among sexes as best as possible (table 5). Because the CTT HybridTags were heavier than the other two transmitters and because we caught fewer females, we only deployed these on males (table 5). We banded 16 adults in croplands and 17 in prairies.

Additional Transmitter Notes

We deployed three types of transmitters: Lotek NanoTag, CTT LifeTag, and CTT HybridTag (table 4). The different transmitters have visual and technical differences that affect future study designs. Two key technical differences are the mass and longevity of the transmitter. We used Lotek NanoTag transmitters weighing about 0.57 g, CTT LifeTag transmitters weighing about 0.47 g, and CTT HybridTag transmitters weighing about 0.65 g. There were lighter versions of the Lotek NanoTag transmitters on the market at the time of this study, but these versions have a shorter battery life; we were using the lightest CTT LifeTag available at the time. We were limited by the mass of transmitters when applying them to hatch-year birds and by the combined mass when adding both color bands and transmitters to lighter adults. The Lotek NanoTag’s longevity is constrained to battery life, which is about 291 days for the transmitter size and transmission interval we were using (NTQB2–5–1; 29-second interval; Lotek). Both models of CTT transmitters are solar powered and have the potential for full annual cycle transmission if the transmitter remains attached to the bird and does not malfunction. The CTT LifeTags are strictly solar powered and are thus restricted to transmitting during daylight hours; the CTT HybridTag has both a solar panel and a rechargeable battery and can transmit 24 hours per day under ideal conditions.

All transmitters were applied using a modified leg-loop harness (Rappole and Tipton, 1991; Streby and others, 2015), but where the transmitter lays on the bird’s back is different for the two brands of transmitters (fig. 11A–B). The CTT LifeTag and HybridTag transmitters rest lower on the bird’s back compared to the Lotek transmitter, with an attachment point at the upper tip of the transmitter if using the manufacturer’s “Flex Tab” (fig. 12A–B). The antenna end of the transmitter, therefore, is not secured to the bird. The Lotek NanoTag is secured on the bird at both the top and antenna end of the transmitter through tubes (an optional feature that can be requested at purchase); therefore, although the two brands attach to the bird at a similar location via the leg-loop harness, the entirety of the Lotek transmitter rests higher on the bird’s back than the CTT transmitters.

The transmitter’s concealment and color while on the bird also varied between the two brands. The CTT LifeTag and HybridTag are more reflective because they contain a solar panel, whereas the Lotek NanoTag transmitter is bright white (figs. 11A–B and 12A–B). Feathers eventually help cover some or all of the Lotek transmitters in adults (fig. 13), but the CTT solar panel stays visible because it is needed to function (fig. 14). We are unsure if these differences affect an individual’s survival or preening ability, visibility to other birds (including predators), or the transmitter’s ability to be detected by a receiver (refer to Jones and others [2024] for more discussion on the topic). We discuss differences in detections with handheld receivers used during a field detection test in the “2023 Reencounters” section.

Adult Birds Captured on Nests

During 2022, we captured 12 adult TBLO on 12 unique nests using a variety of trapping methods; we never captured a complete breeding pair at a nest (table 6). We trialed capture techniques at 23 of the 53 nests that we located in both cropland and prairie habitats (table 7). We used the dropped mist net method (refer to the “Horizontal Mist Nets” section) to capture four of the five incubating females. The fifth incubating female was flushed from her nest into a vertical mist net. As discussed in the “Other Capture Methods” section, the walk-in trap, bow net, and noose mats have limited applicability for captures on nests. We were also able to capture two adult males provisioning food to nestlings using a walk-in trap, though the visibility issues discussed previously are a limitation of this method. All methods used for on-nest captures performed similarly between the two habitat types; visual obstruction by vegetation was the main factor affecting the efficacy of the different methods.

One concern related to trapping TBLO on nests was that trapping might cause nest abandonment. To assess potential abandonment by the captured individual, we tried to return to nests within 1–2 days (if weather allowed) after capture to assess nest status and adult presence. Capture attempts of incubating females were attempted either at or after day 10 of incubation (based on egg flotation) or during the nestling stage to reduce risk of nest abandonment by capturing adults early in the nesting cycle (Winter and others, 2003).

Of the 10 females captured on nests, we observed 4 that continued to attend to their nests (we defined these as “stayed”; table 8). Individuals were assigned this status if the nest was still active on our next nest visit and if we observed the focal adult on or near the nest. One of the four females that stayed was captured on the last day of our field season but was observed incubating 2 hours later after her initial capture.

Two females presumably abandoned their nests after capture, but the cause of abandonment was unknown. In one case, the nest had cold eggs on the next visit (1 day after the capture), and we only detected her once on subsequent visits. The bird was detected using a handheld receiver, but we never obtained a visual of the bird. We did not detect the other female categorized as abandoning nor did we observe her in the area after her initial capture; however, this female was detected after the breeding season during migration (refer to the “Motus Network Detections” section); therefore, she may have still been in the area, but we failed to detect her using the handheld receiver.

Two females and two males were assigned a status of “unknown and not detected” after capture. In all three instances, their nests had failed before the next visit after capture (1–7 days later), and the marked adults were not observed thereafter.

Two females were assigned a status of “unknown and detected” after capture (table 8). In both cases, we observed the marked adult near the nest, which had failed between visits (4–15 days later). One female (female a) was observed on a new nest within 36 m of her previous nest where she had been captured. This second nest was still active at the end of the field season. For the other female (female b), her nest contained dead nestlings, and we detected this female twice near the nest in the week after nest failure. Two other nests in the area also had dead nestlings in the nest cup that week, and we attributed this to a storm with heavy rainfall that had passed through the area after capture of the adult but before our return, which also prohibited a shorter return interval at this nest. We had not captured the females associated with the other two failed nests. It is possible that female b may have stayed on the nest (after capture) as she was still in the area after the weather-related nest failure (table 8).

Hatch-Year Captures

We banded 21 hatch-year TBLO during the 2022 field season (table 5). Most hatch-year birds were banded with only a metal band (n=12); others were banded with a unique color-band combination (n=6) or a transmitter (n=3; table 5). Hatch-year birds included two age classes of young-of-the-year: nestlings (present in the nest cup) and fledglings (present outside of the nest cup). We banded most nestlings with only a metal band in hopes of capturing them later when their mass and age were appropriate for a transmitter. We banded 12 nestlings (cropland: n=5; prairie: n=7) from 4 monitored nests (range: 2–4 nestlings per nest; cropland: n=2 nests; prairie: n=2 nests). An additional nine fledglings (cropland: n=7; prairie: n=2) were located; five were from three known nests, and four fledglings were discovered opportunistically.

We captured four fledglings that were heavy enough for a transmitter. Transmitters were applied to three of these four fledglings, including one from a nest that we were monitoring; the other three fledglings were discovered opportunistically by observing adults in areas without a previously known nest. We chose to deploy transmitters on no more than one fledgling per brood. Two of the three TBLO fledglings fitted with transmitters were detected for almost a week after deployment (detected for 4 and 6 days each) using handheld receivers (refer to the “Handheld Transmitter Reencounters” section). It is possible that these birds were still in the area after this time, but we were unable to detect them because of limitations of the handheld receivers (refer to the “Transmitter Detection Field Tests” section), and limitations associated with private land access that restricted where we could search. Lastly, our ability to find fledglings of appropriate mass was limited by our reduced nest searching and monitoring effort and the high failure rate of nests.

The appropriate age for transmitter application on fledgling TBLO appeared to be 12–14 days old based on mass, feather development, and mobility of birds postdeployment. To stay within our permitted ≤3 percent of an individual’s mass, we deployed only CTT LifeTags on hatch-year TBLO as this transmitter was the lightest of the three units that we tested. This meant that hatch-year birds needed to weigh at least 18.5 g to receive a transmitter (considering transmitter harness material and the metal band). Hatch-year TBLO also needed to be able to flutter-fly (achieve sustained flight for a short distance) but still be able to be guided towards a vertical mist net for capture. In our experience, if the hatch year was still able to be captured by hand or with a hand net, it was generally too light or would likely have trouble maneuvering with a transmitter (fig. 15A–B). Of note, transmitters were too heavy and feather development was too limited to deploy transmitters on nestlings that were still in the nest cup, which may have important ramifications for studies using CTT LifeTags with an objective to evaluate postfledgling juvenile survival. Future study questions focusing on juveniles may require a lighter transmitter that can be applied at an earlier stage of development or other marking and modeling schemes used to identify individuals earlier in their development. The potential effects of transmitters on juveniles and the potential of transmitter removal by adults may need to be considered (Mattsson and others, 2006; Fisher and others, 2010).

Color-Band Reencounters

One way that we relocated marked individuals was by reading their unique color-band combinations using optical equipment (resighting). Obtaining color-band resights can be difficult because of the species’ behaviors during the breeding season (for example, tendency to spend time on the ground, aerial song flights of males). This difficulty can be exacerbated as vegetation grows throughout the season. It was generally easiest to see TBLO legs when birds stood on a rock or dung pat or when they walked to the top of a crop row mound during early season conditions or between crop rows during later season conditions. In the following paragraphs, we elaborate on the various methods (binoculars, spotting scopes, digital single-lens reflex [SLR] cameras, camera traps, and video cameras) we used to resight color-banded individuals (table 9).

Binoculars had limited utility in determining color-band combinations as the magnification (for example, 10 × 42 Nikon Monarch 5 or 8 × 42 Swarovski NL Pure) that we used, in combination with the birds’ skulky behavior, often made it difficult to resolve leg detail. If the bird was close enough (for example, within about 100 feet), the presence of color bands could often be determined, but the precise color-band combination was difficult to discern. Spotting scopes on tripods (for example, 20–60 zoom Nikon Prostaff 5 or Leica Televid) functioned better in this regard as they provided the greatest optical reach of the equipment we trialed. Spotting scopes were most useful early in the season when vegetation was absent in croplands and short in prairies. As the vegetation grew during the breeding season it became more challenging to find and follow birds with a spotting scope to get a clear view of a bird’s legs. In 2023, we determined that spotting scopes were useful for quick assessments to determine if a TBLO was marked, especially for TBLO detected at a great distance. Such information (knowing if the bird is marked) could be useful for directing further efforts to read the color-band combination.

Digital SLR cameras proved useful for obtaining color-band resights. We used a Nikon D5500 with a 70–300-millimeter telephoto lens. This setup was light and easily portable compared to spotting scopes, but still allowed for determination of the presence of color bands on distant, perched TBLO. As vegetation grows, it may be more efficient to use digital SLR cameras for resighting as there are brief lines of sight for determining if a bird is banded amid the taller vegetation. Cameras allow quick snapshots through available sightlines, whereas spotting scopes may require more time to confirm a bird’s markings. Multiple images may be necessary to identify the color and position of all bands; however, the use of digital cameras may require additional time to process images taken in the field and the development of a data storage and archiving plan.

We also used camera traps pointed at an elevated, baited surface to resight banded TBLO (fig. 16A–B). Although this method required time to attract birds to an area, it provided a passive method for reencounters that can be used in conjunction with capture efforts (refer to the “Bait” section). It was unclear how far birds were traveling to and from the baited sites; therefore, further investigation on the actual area being covered by the camera traps at bait sites may be needed. We used a Bushnell Trophy Cam with settings set to take a picture every 5 minutes during daylight hours and anytime when motion triggered. With these parameters, we were able to obtain resights of color-banded individuals and clear images of unbanded TBLO and other bird species. Other brands of cameras may have settings and features that provide better quality photographs, but we did acquire images of TBLO with both the motion triggered and 5-minute interval settings. Researchers may want to balance photograph capture rate with the time needed to assess the photographs during postprocessing. In 2023, no banded TBLO were observed during a 3-day camera deployment, but we did obtain quality photos of unbanded TBLO legs during that short window of deployment. In areas with cattle, we had occasional issues with livestock knocking the camera out of position. Fencing to exclude livestock from the camera vicinity may be a solution to this issue; however, adding additional structures to an otherwise open landscape may need to be carefully considered. Camera traps also may be useful away from bait but would require a lure at the camera location. Deploying cameras near water sources or short-term (that is, for a few days) deployments near audio or visual lures may allow for passive resights of color-banded individuals. Lastly, a combination of a camera trap, bait, and a transmitter receiver may be of use to increase reencounters.

We used small video cameras placed near TBLO nests for ≤30 minutes to resight nesting adults. We were able to successfully resight color bands and get clear images of unbanded TBLO legs (fig. 17A–B). We trialed two cameras in 2022: a Go Pro Hero 8 and a Kodak PixPro (Toy and others, 2017). We obtained resights with both cameras, but both were also used in trials when the bird did not return to the nest during the 30-minute session. We did not know if birds failed to return to the nest because of the camera’s presence or because of the birds’ nest attendance behaviors. The Kodak PixPro camera sat about 14 cm above the ground on a small tripod, whereas the Go Pro camera could be placed on the ground with a camera height of about 4.5 cm. Notably, when placed on the ground, the Go Pro camera had to be set up close to the nest to obtain a clear view because of vegetation obstructing the camera’s view. We suspected birds would be deterred by the proximity of the Go Pro in those situations, and, therefore, we needed to elevate the camera to obtain a clearer view while also increasing the distance of the camera from the nest.

We also tested the idea that a well-camouflaged camera placed next to the nest may be more effective than cameras that require an elevated view placed further away (greater than or equal to 25 cm) from the nest; therefore, in 2023 we trialed a Vsysto helmet camera, a cylinder action camera that can be placed on the ground with a lower vertical profile than the cameras we used in 2022. We placed the camouflaged (painted three-dimensional-printed cover) camera roughly 10 cm from the nest, which was necessary to obtain an unobstructed view of birds returning to the nest. We trialed this camera on a TBLO nest with three 5-day old nestlings present in a cropland field for 30 minutes before retrieving the camera. We were able to see the legs of the adult male and female to confirm both were unbanded (fig. 18A–C). With this camera, we also obtained video of the adults provisioning the nestlings; however, this camera model can overheat and had lower video quality than a similar camera (Fire Cam Mini 1080) that we tested for another project. Therefore, a different camera model may be better suited for this task, but we did obtain resights with our field test. In general, a camera placed near the nest would tie banded individuals to a nest and may be the most effective way to resight a marked incubating female without capturing her. Nest cameras also may be useful to assess if the adults tending the nest need to be captured (for example, unbanded, lost color band, or dead transmitter) or if a large portion of the population is marked. Additionally, this tool could assess if marked birds return to nests after capture attempts. Long-term deployments of nest cameras would, however, require careful thought as to potential indirect effects or biases on predation risk and nest survival (for more discussion on this topic, refer to Richardson and others [2009]). We limited our trials to 30 minutes to minimize disturbance at nests.

We used several methods to resight color-banded birds, and each method varied in both the amount of time required to obtain a resight and in its effectiveness. Of note, the visibility of a transmitter’s antenna aided in focusing resighting efforts for individuals with transmitters as we knew that bird was marked and may also have color bands. Spotting scopes and digital SLR cameras allow for mobile efforts compared to the nest or camera traps, but tall vegetation can hinder resighting capabilities. For longspurs that were particularly difficult to view to determine if they were banded, we played TBLO vocalizations via a small Bluetooth speaker to get the bird’s attention. This method had mixed results but did work on several occasions by increasing opportunities to view the individual at a closer distance. It was also advantageous to place the speaker on bare ground to improve the odds of a TBLO landing in an unvegetated area to improve the view of its legs. Based on our experience, spotting scopes and digital SLR cameras were more effective in areas of bare substrate such as along two track roads, at waterbodies, and at baited sites. Camera traps provide a low-effort opportunity for passive viewing but are limited by a prerequisite lure (bait, audio lure, or possibly water sources) and the distance that birds travel to the lure from their territories. The nest cameras proved effective and may be especially useful when nest monitoring is an objective; however, careful attention to the nest-camera deployment is needed to increase the chances of a clear view of the bird’s legs and to minimize disturbance to the study subject. Future study objectives and site characteristics will likely determine which combination of methods would be most useful to obtain visual resights of color-banded birds.

Handheld Transmitter Reencounters

We used handheld receivers specific to each brand of transmitter to detect radio-marked birds (fig. 19). We detected 19 of 27 deployed transmitters at least once on a different day after initial deployment in 2022. We detected 13 transmitters on multiple days after deployment in 2022. We did not use a standardized method for obtaining reencounters via transmitter detection. In general, we attempted to detect transmitters in and around areas where we fitted TBLO with a transmitter previously. We did not detect any transmitters in areas other than where we initially deployed them in 2022; however, we noticed that transmitter detection range with the handheld receivers was limited, particularly when a transmitter was near the ground (refer to the “Transmitter Detection Field Tests” section). Additionally, we were restricted to areas where we had obtained land access. It is possible that a TBLO with a transmitter may have moved to a nearby field that we did not have permission to access, and, thus, we were less likely to detect that bird’s transmitter.

In 2023, we returned to areas that we had marked individuals in 2022 and areas that had historical records of TBLO that we did not visit in 2022 (for example, other sites from Swicegood [2022] and eBird locations). We did not detect any transmitters using either brand of handheld receiver. The Lotek NanoTags, with a roughly 291-day battery lifespan, were not expected to be detectable (May 3, 2023, was the predicted last day the latest deployed 2022 Lotek transmitter would still be active). At sites we did not have permission to access (in both years), we only attempted to detect TBLO from public roads which limited our ability to detect transmitters in those areas.

Transmitter Detection Field Tests

We completed three different field tests to assess transmitter detectability. In the first test, we assessed the range for the handheld receivers to detect transmitters on the ground or about 2 m in the air. In the second, we assessed detections by the stationary Motus receiving station for transmitters held about 5 m in the air in areas where transmitters were deployed in 2022. Lastly, we tested the use of a CTT Node to detect transmitters about 50 m away.

We completed a field test to assess transmitter detection range with the handheld receivers by having one person who was holding a transmitter walk away from a second person that was holding the handheld receiver. To determine if the transmitter could be detected by the handheld receiver, the person with the transmitter would stop and hold the transmitter in the air (about 2 m above the ground), followed by holding the transmitter to the ground (mimicking an incubating female, prefledging hatch-year bird, or any individual on the ground). We repeated this procedure roughly every 100 m. We recorded if a detection was recorded, the distance from the receiver, and the signal strength of the detection at various distances (table 10). We used the Lotek SRX1200 M1 receiver to detect Lotek transmitters and the CTT Locator to detect CTT transmitters. At about 200 m, neither brand of transmitter was detected when the transmitter was held near the ground. One key difference between the two brands of transmitters was the ability of the receiver to identify an individual transmitter. For CTT transmitters, the identity was always known if it was detected. For Lotek NanoTags, the transmitter can be detected when the signal is strong, but the transmitter identity can remain unknown when the signal is weak with the receiver we used; therefore, sometimes we detected a Lotek transmitter without knowing which transmitter it was until we were closer. The ability to detect the transmitters seemed dependent on multiple factors including, but not limited to, whether the transmitter was moving, transmitter height above the ground, and transmitter antenna direction (pointing toward or away from the receiver). Male TBLO may be easier to detect than either hatch-year or female birds because of their aerial song displays.

In 2023, we used both CTT and Lotek transmitters (same versions as 2022 field efforts) to trial the Motus receiving station in northern Valley County, Mont. (https://motus.org/data/receiverDeployment?id=9124). We turned the transmitters on and off at several locations near and within study sites where we deployed transmitters in 2022. We also placed transmitters on a long pole and stood in a truck bed for 5–10 minutes, elevating the transmitter to roughly 5 m above ground to mimic heights of flying or displaying TBLO (fig. 20). Both transmitters were detected but only on the day that we tested them within eyesight of the Motus station, which is the expected behavior given line-of-sight conditions. On all other days, the transmitters were not detected based on publicly available data on the Motus website. Of note, several locations we tested were outside the estimated antenna ranges as indicated on the Motus website; however, other locations were within the antenna ranges, but topography and our limited testing heights may have prevented detections.

We also completed transmitter detection tests at a water source using a CTT Node V2, which is a temporarily deployed solar-powered receiver station. We simulated a TBLO flying towards a small waterbody in cropland habitat and taking a drink at the water (active transmitter on a long pole moved close to ground near water). The transmitter was detected by the Node from each of the four cardinal directions (north, south, east, west). The waterbody was small such that the transmitters were within 50 m of the Node during the simulated drinking. We also tried this method at a larger waterbody in a prairie site, but we did not use a pole to simulate a flying or drinking bird. Results were similar between the two trials. Placing Nodes in areas of known TBLO use, like standing waterbodies, or near bait may be a useful method for passively reencountering CTT transmitters. Although our testing was limited, the use of nodes or other temporarily deployed receivers may be helpful in reencountering TBLO. Of note, the manufacturer has discontinued the model of CTT Nodes we used, but a new version is planned to be available sometime in the future.

2023 Reencounters

Most of our efforts in 2023 were focused on reencountering previously marked individuals in areas we had previously marked TBLO in 2022. Where we had permission to access land (in both years), our two-person field crew walked slow transects through TBLO habitat using spotting scopes, binoculars, a digital SLR camera, and (or) handheld receivers to attempt to reencounter TBLO. As birds were encountered, we stopped to scan TBLO legs with optics and periodically listened with handheld receivers. We estimated that we visually encountered (clearly saw the legs of) more than 200 unique adult TBLO across all sites in the 2023 field effort. Most birds encountered were males (~83 percent); this is not surprising as sex-specific behaviors of males, such as display flights, make them easier to detect. We did not detect any transmitters with the handheld receivers. Although we did explore areas that were not visited in 2022, we were limited to view these areas of TBLO use from public roads. In these areas, we did not obtain any additional resights of marked or unmarked TBLO; the distance was too far to obtain clear views of TBLO legs from the road, even with spotting scopes, nor did we detect any transmitters with handheld receivers.

We detected one previously banded TBLO, a male with a nonfunctional Lotek transmitter and color bands seen at a prairie site (fig. 21). We tried on two days to capture this male to remove the transmitter, but we were unsuccessful. Unfortunately, we were unable to identify the bird as a unique individual because one of its color bands had fallen off since we marked the male in 2022. Based on the color bands the bird retained, the bird’s sex, and the type of transmitter the bird carried (Lotek), we were able to narrow the identity of this male to one of three individuals that we banded nearby in this same prairie site in 2022, suggesting it did return to the same general area. The marked individual we resighted in 2023 maintained a consistent territory during our 2023 field season which gave us multiple chances to resight and photograph the bird. We also could quickly determine which individual we were targeting when other males entered the area because the marked bird’s transmitter antenna was visible when the bird was flying (and occasionally when the bird perched on a rock or dung pat).

Motus Network Detections

During our 2022 field season, no Motus receiving stations were operating within our study area. In October 2022, a single Motus station was installed in northern Valley County, Mont. (fig. 1), but the station has not detected any TBLO with transmitters at the time of this report. Within the Great Plains, the number of fixed Motus receiving stations has been increasing since roughly 2020, and a map of available receiving stations through time is available at https://motus.org/data/receiversMap.

As of January 27, 2025, four different TBLO with transmitters from this study have been detected by two Motus receiving stations. Detections were during southbound migration (n=2), at stationary nonbreeding sites (n=1), and during northbound migration (n=1). In this section, we describe the birds’ original captures and subsequent detections.

An adult female was detected once on October 20, 2022, at 7:59 p.m. local time, at a Motus station near Karval, Colorado. This detection likely was during southbound migration, as the area is not a known breeding or stationary nonbreeding area for the species. The female was captured with a horizontal mist net in cropland on July 14, 2022, on a nest containing 8–10-day old nestlings. She received a Lotek NanoTag and a USGS metal band.

The second TBLO detected by Motus was an adult male that pinged the same station near Karval, Colo., on November 6, 2022, at 8:19 a.m. local time, likely during southbound migration. This individual was captured and banded at a prairie site on July 13, 2022, using a horizontal mist net over an audio lure. He received a Lotek NanoTag and a USGS metal band. We did not detect the transmitter again after the bird’s initial capture.

The third TBLO, an adult female, was detected at a Motus station on the Mimms Ranch near Marfa, Texas. She was captured and fitted with a CTT LifeTag, color bands, and a USGS metal band in a prairie site on July 21, 2022—our last day of field efforts—using a horizontal mist net on a nest containing a 1-day-old nestling and three eggs. She was detected most days from November 30, 2022, to January 14, 2023, ranging between 9:12 a.m. to 6:36 p.m. local time on the Mimms Ranch. This is a known nonbreeding area for TBLO.

The fourth TBLO, an adult female, was detected on April 11, 2023, at 6:45 a.m. local time, at the same Motus station near Karval, Colo. This detection likely was during northbound migration given the time of year. This female was captured using an array of two-shelf mist nets near an established baiting site on June 3, 2022. She received a CTT LifeTag, color bands, and a USGS metal band. She was detected once on June 27, 2022, using a handheld receiver during our 2022 field efforts. She was not detected during our 2023 field efforts.

It is possible that new detections will have been reported since the release of this report. To view detections for this project, visit the Motus website: https://motus.org/data/project?id=423.